UK Transit visa.. not getting down the flight

[latkrish]

I am in H1-B status and going to India to get my passport stamped. I am taking Air-India flight from JFK-Chennai with no stopovers. However the flight will halt for an hour in London for fueling.
Do I need to get a transit visa for London even if I don't have to get down the flight?
If I need to, then do I apply for Visitor in Transit Multiple Entry - 6 months or
Direct Airside Transit visa?

Any help is greatly appreciated.

Thanks a lot.

Regards,

Latha.